Aft structures of marine vessels

ABSTRACT

A stern construction for a ship having a propeller with detachable blades includes a passage over the propeller through which the blades can be lifted into the ship. The propeller boss is made integral with the shaft and the blades have flanges which are bolted in recesses in the boss. Provision is made for locating the blades at a required pitch and for purging the space between the blade and the boss as each blade is fitted.

United States Patent AFT STRUCTURES OF MARINE VESSELS 10 Claims, 7 Drawing Figs.

US. Cl 115/34, 1 14/57 Int. Cl B63h l/14 Field of Search 1 14/56, 57; 1 15/34 [56] References Cited UNITED STATES PATENTS 20,751 6/1858 Webster 115/34 FOREIGN PATENTS 11,822 1889 Great Britain 115/34 Primary ExaminerTrygve M. Blix Att0rneyWoodcock, Washbum, Kurtz & Mackiewicz ABSTRACT: A stern construction for a ship having a propeller with detachable blades includes a passage over the propeller through which the blades can be lifted into the ship. The propeller boss is made integral with the shaft and the blades have flanges which are bolted in recesses in the boss. Provision is made for locating the blades at a required pitch and for purging the space between the blade and the boss as each blade is fitted.

' PAIENTEHJANZBIBYI' 3557 744 saw 3 OF 3 AFTSTRUCTURES OF MARINE VESSELS The present invention relates to stem constructions for marine vessels having detachable propeller blades, to the mounting of the propeller blades on the boss, and to the securing of the boss to the propeller shaft.

Existing propeller constructions are of various types but all give rise to difficulties when the propeller has to be removed for inspection or replacement of the propeller itself or the propeller shaft and its bearings. As vessels get larger the dif ficulties of handling the propellers increase and inspection and maintenance requires periods in dry dock'which become less and less tolerable as the capacity of vessels increases and the value of the load carried becomes greater. Many existing propellers have the blades integral with a boss which is secured to the end of the propeller shaft by a nut. The difficulties of handling a large unitary propeller are reduced by providing separately cast propeller blades whose roots have flanges for attachment to suitable facings machined in the periphery of the boss casting. Detachable propeller blades are also used in adjustable pitch propellers.

As the propeller or propellers with marine vessels are usually located under the counter of the vessels, movement of the blade to be replaced from its working position is normally a difficult operation because it involves taking the blade out laterally under the counter before lifting the blade upwards. This usually involves the use of multiple slings suspended from special lugs attached to the shell of the vessel beneath the counter. This method of removal is by its nature clumsy and becomes less accessible as the size of propeller increases such as is occurring with propeller blades for very large tonnage bulk carriers. With very large vessels, such as oil tankers or other bulk carriers, docking facilities are limited and it becomes desirable to be able to change the propeller blade with the ship afloat and without assistance from shore facilities.

In accordance with the present invention there is provided a marine vessel having a propeller projecting under an overhung stern, characterized in that the propeller has dismantlable blades and the overhung stern has a closable passage located over the propeller through which the propeller blades can be passed between the vessel and the propeller boss.

The passage may be closable by a removable watertight cover arranged above the fully-loaded water line or the maximum water line at which blade replacement will be carried out. To reduce undesirable stress concentrations in the hull structure the passage and the cover may be of oval shape. A fairing is preferably attached to the cover to continue the outline of the stem at the lower end of the passage. The passage may take the form of a trunk which extends from outboard to any convenient floor within or on the vessel.

The provision of this passage allows a blade to be lifted into the vessel by a simple hoist and deposited on a chosen floor of the vessel. If the passage extends up to the deck of the vessel it is possible to use a'cargo crane or derrick for removing the cover and handling the propeller blade. After the necessary work has been carried out the blade or a replacement blade can be lowered into position through the passage and fastened to the boss.

The passage can also accommodate ladders for access, power supply lines for pneumatic or hydraulic tools used in changing the blades, and folding stages which can be lowered through the opening to form a working platform supported, for example, by the propeller boss itself.

To simplify the propeller construction and thereby reduce the necessity for inspection and maintenance the propeller boss is preferably formed integrally with the propeller shaft. The propeller blades can have circular flanges attheir roots which are located in corresponding recesses in the boss by spigots projecting centrally from the recesses. The pitch of the propeller blades can be adjusted by fitting dowels in a selected pair of sockets in the faces of the blade root and boss recess to establish the required angular position. Preferably means are provided for producing a flow of purging fluid across the mating faces of the blade root and the boss during assembly to remove foreign matter and displace contaminated water. To this end a sealing ring is preferably arranged between the peripheries of the blade root flange and the recess in the boss and inlet and outlet valves are provided for the purging fluid.

The invention will now be described in more detail with the aid of an example illustrated in the accompanying drawings, in which:

FIG. 1 is an axial cross section of part of a propeller shaft and boss with detachable propeller blades,

FIG. 2 is a transverse section on the line Il-Il of FIG. I and shows the line of section of FIG. 1 at H,

FIGS. 3 and 4 are sections on the line III-III and lV-IV, respectively, in FIG. 5, which is a plan view of the blade root flange,

FIG. 6 is a diagram of the stern construction in accordance with the invention for facilitating dismounting of the propeller blades, and

FIG. 7 is a section on the line VII-VII of FIG. 6.

FIG. 1 shows a propeller boss 1 which is formed integrally with a propeller shaft 2 which may, if necessary, be a hollow shaft as shown by the broken lines 3. The boss and shaft can be formed by forging or casting the whole in one piece or by permanently welding the two components together during manufacture. The boss is a generally cylindrical body having a larger radius than the shaft 2 and has an internal cavity 4 which is of approximately spherical form. This cavity serves to minimize weight and to reduce stress concentrations in the transition between the shaft and the boss. The integral boss and shaft construction allows the boss to be shaped to the best functional advantage, in particular in order to reduce the distance between the center of gravity of the propeller and the aft end of a stem-tube bearing 5 supporting the shaft 2 since this affects the bending stresses on the shaft and the whirling characteristics.

The propeller boss 1 has circular recesses 7 for receiving circular flanges 8 on the roots of the propeller blades 9. Each recess 7 has a central locating spigot 10 which fits within a socket in the blade root and thus an annular seating is formed for the blade root flange 8. Annular sealing rings 11 are located between the peripheries of the flange 8 and the recess 7. The flange 8 has a number of bolt holes 12 in which are fitted bolts 13 which secure the blade to the boss.

Regions 6 of the boss 1 are protected from corrosive attack by sea water by means of a sleeve 14 which forms the rotating member of a stern seal having a stationary sealing ring assembly 15. Other external faces of the boss may be protected from sea water attack where required by the application of surface coatings or deposition of corrosion resistant materials on the surface.

As shown in FIGS. 3 and 5 the exact pitch of the blades is determined by a pair of locating dowels 16 which are received in sockets 17 in the mating faces of the flange 8 and the recess 7. By the provision of alternative pairs of accurately-positioned sockets 17 the pitch of the blades can be set to the required valve during assembly by placing the dowels I6 in the appropriate sockets.

When refitting a propeller blade, especially when this is done at sea, it is important to ensure a clean joint free from corrosive elements and for this purpose provision is made for maintaining a flow of purging fluid across the mating faces of the blade root flange 8 and the recess 7 and around the securing bolts 13 and the dowels 16. The purging fluid, which may be air, fresh water, or other liquid and may contain a corrosion inhibitor, is supplied under pressure and serves to remove foreign matter and to displace sea water. The purging fluid is supplied to a space 18 (FIGS. 3 and 4) between the spigot 10 the blade root through a nonretum inlet valve 19. From the space 18 it flows by way of channels 20 in the periphery of the spigot 10 to an annular channel 21 around the base of the spigot. It then flows radially outwards through channels 22 in the under face of the blade root, past the dowels 16 into an annular passage 23 below the sealing rings 11 (FIG. 5). The

sockets 17 for the dowels 116 have semicircular grooves 24 extending axially from the channels 22 to ensure a flow of purging fluid around the ends of the dowels.

From the passage23 the purging fluid flows by way of channels 25 to the bolt holes 12. The empty bolt holes 112 are closed off by plugs 26 to ensure maintenance of a sufficient pressure of purging fluid when the blade root is first placed in position. At this stage purging fluid flows freely across the mating faces of the blade root and the boss but thereafter as the bolts are inserted and tightened flow is confined to the passages and channels described. As end bolt 12 is tightened a sealing washer 26 on the bolts takes effect and the purging fluid supplied through the channel 25 is forced to flow down around the threads of the bolt 13 to the space under the bolt, from which it passes through an axial bore 27 in the bolt and out of a bleed valve 28 in the bolt head.

In a an alternative purging system not illustrated in the drawings the bolt holes are interconnected in series and the last bolt hole to receive its bolt is connected to a separate outlet valve in the blade root.

FIG. 6 shows the propeller with its boss and detachable blade 9 mounted under the overhung stem or counter 29 of a vessel forward of a rudder 30. Directly above the propeller there is a vertical passage in the stem formed by a rectangular trunk 31 opening at its upper end at a convenient flooring 32 and continued at its lower end by a trunking 33 of oval cross section. The oval trunking 33 is closed by a watertight cover 34 which carries a fairing 35 which fills the trunking 33 and continues the contour of the stem 29. The trunking 33, which is oval in order to minimize the cross-sectional dimensions and to reduce stress concentrations in the hull structure, is, as shown in FIG. 7, of sufficient dimensions to allow a propeller blade 9 to be lifted through it after removal of the cover 34.

The cover 34 is preferably disposed above the fully-loaded water line of the vessel so that it may be removed to enable work to be carried out on the propeller even when the vessel is in a seaway and is fully loaded. However a lower position can be used and if necessary the cover can be lifted above the water line by adjusting the ballast or loading of the vessel.

A simple traveling hoist 36 mounted within the vessel enables the cover to be removed as indicated in chain lines in the drawing and thereafter is used to lift a propeller blade 9 through the trunking 33 and trunk 31 and deposit it on the flooring 32. As previously mentioned folding staging (not shown) can be mounted in the trunk 31 to facilitate access to the propeller and the supply lines for pneumatic or hydraulic tools also pass through the trunking. For removing or tightening the bolts 13 power-operated torque wrenches can be used and to facilitate their use the bolt holes 12 are provided with notches 37 to take up the reaction forces from the wrench.

It will be seen that the arrangements described greatly simplify propeller inspection and repair and stem gear survey work and enable these operations to be carried out without drydocking, using simple lifting facilities which are carried by the vessel. If necessary the operations can be carried out by the ships own personnel providing they are equipped for underwater work.

lclaim:

l. A stern construction in a marine vessel comprising a propeller shaft, a propeller boss on said shaft, propeller blades having flanges at their roots, mating faces on said flanges and said boss, and bolts detachably securing said blade flanges to said boss, and means for providing a flow of purging fluid between said mating faces during attachment of each of said blades to said boss.

2. A stern construction as claimed in claim 1 in which said means for providing a flow of purging fluid comprise an inlet in each of said blade flanges for the admission of purging fluid under pressure and at least one outlet valve in one of said bolts.

3. A stern construction as claimed in claim 1 having a seating in the root of each blade and a locating spigot projecting from the boss and cooperating with said seating to locate the blade and to define a space between said spigot and said seating,said means for providing a flow of purging fluid comprising an inlet valve in said blade flange communicating with said space.

4. A stern construction as claimed in claim 3 having recesses in the propeller boss in which said blade flanges are received, a sealing ring between the periphery of each blade flange and the boss recess in which it is received, passages for the flow of purging fluid from said space across the mating faces of the blade flange and the boss, and at least one outlet valve for the purging fluid.

5. A stern construction as claimed in claim 4 wherein each of the securing bolts has an axial bore therein and an outlet valve for purging fluid in said axial bore.

6. A stern construction as claimed in claim 1 wherein said boss is integral with said shaft.

7. A stern construction as claimed in claim 1 having a stern structure overhanging said propeller, a closable passage in said stern structure opening over said propeller boss, said passage being constructed for the passage of said propeller blades, and means for lifting said blades through said passage.

8, A stern construction as claimed in claim 7 comprising a removable watertight cover for closing said passage, said cover being disposed in said passage above the waterline and having attached to it a fairing continuing the outline of the stern structure at the lower end of the passage.

9. A stern construction as claimed in claim '1 having sockets in said propeller boss and blades and dowels received in said sockets and locating said blades with respect to said boss.

10. A stern construction as claimed in claim 9 having additional sockets for receiving the dowels, whereby the pitch of the blades may be adjusted. 

1. A stern construction in a marine vessel comprising a propeller shaft, a propeller boss on said shaft, propeller blades having flanges at their roots, mating faces on said flanges and said boss, and bolts detachably securing said blade flanges to said boss, and means for providing a flow of purging fluid between said mating faces during attachment of each of said blades to said boss.
 2. A stern construction as claimed in claim 1 in which said means for providing a flow of purging fluid comprise an inlet in each of said blade flanges for the admission of purging fluid under pressure and at least one outlet valve in one of said bolts.
 3. A stern construction as claimed in claim 1 having a seating in the root of each blade and a locating spigot projecting from the boss and cooperating with said seating to locate the blade and to define a space between said spigot and said seating, said means for providing a flow of purging fluid comprising an inlet valve in said blade flange communicating with said space.
 4. A stern construction as claimed in claim 3 having recesses in the propeller boss in which said blade flanges are received, a sealing ring between the periphery of each blade flange and the boss recess in which it is received, passages for the flow of purging fluid from said space across the mating faces of the blade flange and the boss, and at least one outlet valve for the purging fluid.
 5. A stern construction as claimed in claim 4 wherein each of the securing bolts has an axial bore therein and an outlet valve for purging fluid in said axial bore.
 6. A stern construction as claimed in claim 1 wherein said boss is integral with said shaft.
 7. A stern construction as claimed in claim 1 having a stern structure overhanging said propeller, a closable passage in said stern structure opening over said propeller boss, said passage being constructed for the passage of said propeller blades, and means for lifting said blades through said passage. 8, A stern construction as claimed in claim 7 comprising a removable watertight cover for closing said passage, said cover being disposed in said passage above the waterline and having attached to it a fairing continuing the outline of the stern structure at the lower end of the passage.
 9. A stern construction as claimed in claim 1 having sockets in said propeller boss and blades and dowels received in said sockets and locating said blades with respect to said boss.
 10. A stern construction as claimed in claim 9 having additional sockets for receiving the dowels, whereby the pitch of the blades may be adjusted. 